You can create/retrieve the DATADOG_API_KEY from your account on this page.
API Key, not application key.

You can optionally set additional percentiles for your histogram metrics. By default
only 95th percentile will be generated. To generate additional percentiles, set all
persentiles, including default one, using env variable DATADOG_HISTOGRAM_PERCENTILES.
For example, if you want to generate 0.95 and 0.99 percentiles, you may use following
command:

Credits

This buildpack was heavily inspired by the heroku-buildpack-apt code, as well
as many others from Heroku and @ddollar.
We leverage the same type of process runner that the Datadog Docker container
uses, with a couple of modifications.